As promised, here is the prelim. report on my engine oil sump preheater.

Test conditions:--
Ambient temp, -2*C. Clear weather. Urban/interurban. Driving style; conservative, fuel efficient. Traffic; heavy. S-type 2.7D. 122,000mile.

The first item tested was a radiant lamp projected against the oil sump (dark painted metal) of 400watt. power. This will be about 398watt of heat. This was very slow and not too effective. This was abandoned as it became clear that Kw/hours rather than watt/hours were required.

The second item tried was much better and is now in permanent use. It consisted of a 1Kw spiral element (ex. cooker) held against the steel sump with a powerful spring, the element being backed by a stainless steel disc of 16G. thickness and 6" diameter. No drilling of anything. Trial and error determined that 2Kw/hours is about right for a morning start. A timer was used for convenience, switching on while the tester was in bed.

Readings:--
Previous two mpgUK readings averaged. 22mpgUK.
This reading so far after 25mile. 35mpgUK.(computer).
Usual readings are brim-brim method.
Cost of power; UK on peak, abt. 25pence.

I will provide my construction techniques later. At the moment the intention is to improve the mpg. figure during the cold running period, an especial problem due to the heat efficiency of diesels with their very slow natural warm-up. Current price for diesel in UK is £6/gallonUK

Other things noticed: The glowplug light on dashboard went out quickly and engine cranked fast during cold startup, firing immediately. This must indicate lower engine friction due to hot oil. The hot oil was assessed simply by withdrawing the dipstick and "fingering" it's temperature. Very ad hoc.
The average mpg. indicator from computer is handy for making a running assessment of what's going on. This showed the best way to drive these cars from cold is at 40 to 50mph. This achieves the quickest, safest warmup period. With this type of heater, the car's interior heater gets warm only slightly faster, as to be expected. It's not a block-heater.

Money spent? Around £10/$16. Cost-effective? Oh, definitely!
Leedsman.

 

Hi Leedsman

Interesting approach to engine pre heating. Have you considered one of the heating mats that can be stuck to the sump pan?

Is your Webasto supplementary heater working correctly? I am looking into fitting a timer to fire the Webasto for a period before starting the car to have the same effect.

 

Leedsman....firstly let me say kudos to you for your experimental type of DIY work in this field

As a diesel driver ( Audi A6 ) with poor starting on extreme cold conditions in the Central belt of Scotland, I for one read with interest.

I would be most appreciative, as I'm sure other diesel engined car owners would be, of a good write up possibly with pics if you have the time / inclination to do such a thing for the forum?


Thanks for your post

 

As promised, here is a more accurate report:-

Following a brim-brim diesel fill, the actual mpg came out at 29.4 versus around 22 in cold weather (around 0*C). The computer indicated 30.0 here.
Of course, same itinerary, same driver. So it's safe to say that getting summer mpg in winter means the sump heater is an economic plus, even versus installation cost of probably nothing for a real DIYer, or around £10 for others.

Hints and tips for installation:-

Be careful about fire risk: When cutting the hole out of the undertray, make it a bigger than required. This larger hole has a spin-off advantage -- it's very easy to change the sump oil! Check that the radiant heat from the heater does not melt anything by proper testing and checking over a period.

The most time is taken by cutting out the said hole. A small pair of tinsnips was as good as anything, using a wood-saw hole cutter for the corners. This makes for a neat job, but you have to be careful you don't drill into anything behind the undertray! So the projection of the drill in the hole cutter needs to be as small as poss. You would have to do this to install any heater, as it's not safe to have the undertray too near the heat source. I did not remove the undertray from the car, but I suppose if you have time you could do that. The Oxo cube sound deadening fastened to the backside of the undertray was a pig to cut through.

The heater element used was from an electric cooker, about 5.5" in dia., of 1Kw. power backed by a stainless steel disc I made of 6" dia. to keep the heat against the sump. I.e. the disc facing you, not up against the sump.There are various ways of affixing the element/disc assy against the sump, I used a heavy spring, ex. 15mm pipe bender, and some easy-flexible rodding at each end to affix it to some metal pipes I found there. This will of course vary from car to car, you'll have to use your ingenuity! As a back up to the spring losing it's temper with the heat, I put some rodding through the centre of the spring too, tightening it in the time honored way with a pair of pliers. It's unfortunate the Jag. sump is not quite flat.
If used on another car with a flat sump, probably the cast iron kind of cooker heater plate might also be appropriate, but you still will need the smallest you can get. The construction method used required no holes drilled in vital parts, no dis-assembly of anything.

Almost as an afterthought, I decided for safety's sake to drop the voltage to the heater to 130volt, as I happened to have a big transformer, and leave it on for more than a couple of hours. I just didn't like the bright orange glow after half an hour coming from the spiral element of the heater.
Of course the heater is operated via a timer, this time for 3 hours. You need approaching TWO Kw/h to do any good. If you use one of those "stick-on packages" available on the market, it must have enough power in terms of wattage. If it's only 100watts or so, forget it! You'd have to have it on from now 'til Doomsday to have any effect. The pre- heater will lose SOME heat to the air, but it will rise up the engine itself, heating that part a little.

As for wiring, the flexible cable to the heater must be the best heat-resistant kind, meaning butyl rubber insulation. Crimp-tags are universally used here, so you'll need a couple. An IEC* connector and plug assy. was used at front of car on the plastic strip underneath, mounted in such a way that if the driver forgot it was still plugged in, reversing the car would simply pull out the plug. This driver hasn't forgotten yet! The mounting is out of the way of the rain. Caution here, if you're not too hot electrically (no pun) get an experienced electrician to help.
*This type of connector looks exactly like a kettle plug.

So far the heater has worked as expected for about ten separate cycles with no sign of any trouble. It can't be as good as a water jacket preheater as that will provide some heat inside the car from its own heater, but it doesn't cost £250 plus and a lot of work fitting it.

If you use a paraffin/kerosene sump heater, they aren't bad, and awfully convenient (once you've cut a hole in the undertray). but there is a caution to be observed. Only use the type WITH A METAL GAUZE over the naked flame. This works like a miner's safety lamp and stops any fires/explosions should there be a leak of petrol.

A big advantage of preheating the sump oil not mentioned so far is the much better protection of engine's working parts during the 1st few minutes of operation when cold. This is well known in engineering circles to be where 90% of engine wear happens. I have also replaced the sump oil with full synthetic as it was due a change. I went for 0W30 for slightly better cold circulation, but the thumb and finger test on the dipstick oil didn't seem to show much difference between the 5W30 old oil and the new 0W30 oil.
The engine starts faster when preheated, therefore reducing wear on the starter motor. As I now switch off the engine when stalled in traffic, this is useful. Ok, call me a hypermiler if you like! Who wouldn't be at over £6 gallonUK?
Wishing you all success if you fit this DIY device.

Leedsman.